The present invention relates to a pipette for operating a syringe.
The pipettes for operating a syringe discussed here serve for discharging liquids taken up into the syringe in several steps. They are also called dispensers or repeater pipettes. At the lower end of a bar-shaped housing, these pipettes have a fixture for a flange of a cylinder of the syringe, and in the housing a displaceable fixture body with a piston fixture for the upper end portion of a piston rod of a piston of the syringe. The syringe can be inserted with the flange and the end portion of the piston rod through axially oriented openings of the fixtures. The flange and the end portion are held in the fixtures by means for detachable holding, which are for instance configured as spring-tensioned gripping levers. Further, the pipette has means for displacing the fixture body, which permit to draw the piston partially out of the cylinder in order to aspirate liquid into the syringe, and to push it stepwise into the cylinder for stepwise discharge of liquid.
The documents DE 2926691 C2 and U.S. Pat. No. 4,406,170 A, the entire contents of each of which are incorporated herein by reference, describe means for displacing the fixture body in the housing. These comprise a draw-up lever, connected to the fixture body and projecting out of the housing through a straight slit, for aspirating liquid into the syringe by moving the fixture body away from the fixture. They further comprise a tooth bar pawl device for stepwise piston forward movement by a reciprocating metering lever. A pivotal pawl is bearing mounted on the metering lever. The tooth bar is connected to the fixture body and arranged in the pivot region of the pawl. An adjustably movable covering more or less covers up the tooth row on the tooth bar, in order to limit the engagement of the pawl into the tooth bar when the metering lever is swung. Further, the tooth bar is designed with a contour, by which the covering can be moved away from the tooth bar when the piston is in an advanced position, so that it prevents the pawl from engaging with those teeth of the tooth bar that are not covered. Through this, it is prevented that a residual amount is discharged from the syringe, which is smaller than the metering amount which is to be discharged in each metering step.
Further developments of the means for displacing the fixture body are described in the documents DE 4437716 C2, EP 0679439 B1 and U.S. Pat. No. 5,591,408 A, the entire contents of each of which are incorporated herein by reference.
Further developments of the means for fastening are described in the documents EP 0656229 B1 and U.S. Pat. No. 5,620,660 A, the entire contents of each of which are incorporated herein by reference. The documents EP 1724020 B1 and U.S. Pat. No. 7,731,908 B2, the entire contents of each of which are incorporated herein by reference, describe a further development of the fastening devices which permits to detach the syringe from the pipette using only one hand.
The documents EP 0657216 B1 and U.S. Pat. No. 5,620,661 A, the entire contents of each of which are incorporated herein by reference, describe such a pipette with a sensor for gauging protrusions and deepenings on the syringe flange and associated syringes. The sensor serves to determine the size of the utilized syringe. On the basis of the set step width, an electronics determines the amount of liquid that is discharged in each discharging step. This is indicated on a display.
In a functional embodiment of the pipette, the fixture body is fixedly connected to a rigid cover stripe, which covers the slit from the inside. The cover stripe extends from the fixture body towards the upside, so that it covers only the slit above the draw-up lever. Below the draw-up lever, there is no sufficient space for a further cover stripe. When the draw-up lever is thrust towards the upside, the cover stripe moves to the upside in the housing, and the slit opens below the draw-up lever. In the known pipette, unintended movement of the fixture body and of the draw-up lever connected thereto are prevented in that the fixture body is braked by two elastic hoses which are disposed in the housing of the pipette.
The opened slit permits insight into the casing's interior and also the intrusion of dirt into the housing, which contaminates the mechanical and, as the case may be, the electronic components of the pipette.
The document DE 32 11 271 A1, the entire contents of which is incorporated herein by reference, describes a slide bar control device with slits on the activation elements for heating and venting, in air conditioning apparatuses of motor vehicles in particular. In the slide bar control device, a tape is attached behind the slit or behind the slits, respectively, whose ends are fastened on the base body. The tape is guided through a breakthrough of an actuating lever of the slide bar control device. The tape is disposed at a distance to the slit, so that there is a cavity between slit and tape through which dirt can enter the base body. The tape prevents exterior light from leaving the slide bar control device, and at the same time, it reduces contamination of the inner construction.
The document DE 195 41 628 C2, the entire contents of which is incorporated herein by reference, describes a sliding controller of for instance a sliding variable resistor, or for changing the tension of a spring in a mechanical system, or realised as a program selection lever for an automatic gearbox in motor vehicles. The sliding controller has a housing with a slit, and a sliding block movable in and along the slit, with a take-up side and a take-along side attached thereto and extending through the slit. The sliding controller has a flexible tape extending only in the slit direction. The tape runs above the slit in a groove on the side of the housing directed towards the take-up side and extends across a recess in the sliding block. At its ends, the tape is fixed on the housing, wherein the distance of the fixation points is smaller than the length of the tape extending between them. The tape seals the slit at those positions of the slit where the sliding block is not present. Due to its arrangement at the outer side of the housing, the tape may easily be contaminated and damaged. In one embodiment, the recess in the sliding block is realised by a laterally formed slit in the take-up side of the sliding block. The lateral arrangement of the slit permits lateral exit of the tape. Moreover, it compromises the outer appearance of the sliding block. According to another embodiment, the sliding block is formed by two essentially symmetric halves bearing against each other, which consist of one half at the take-up side and one half at the take-along side, wherein the recess is formed by slits in the contact surface of each one of the two halves, with a depth corresponding to at least half the width of the tape. The split of the sliding block into two symmetric halves necessitates sumptuous assembly, because the halves must be thrust onto the narrow sides of the tape. Moreover, the outer appearance of the divided sliding block is compromised.